This research assesses individual differencesin age-related changes in the neural system as they relate to mechanisms of executive control over memory. Prior research has shown that in groups of healthy older adults, there is a large range of variability such that some individuals retain relatively intact neural responses and behavioral performance compared to younger adults, while other individuals show impairments. These age-related effects are often apparent in tasks involving executive control mechanisms, such as inhibition of unwanted responsesor information, conflict detection, source monitoring, and control over interference. Recently, it has been suggested that these various types of executive control reflect a single underlying mechanism, contextual processing, that is affected by aging. Using neuropsychological and behavioral measures of executive control, this proposal attempts to identify those older adults likely to possess intact functioning and those likely to experience deficits infunction. Having identified subgroups of older adults who are intactor dysfunctional, this research uses fMRI and structural MRI to test whether specific neural structures underlie individual differences within the aging population. Specifically, it examines age-related changes in the anterior cingulate cortex, prefrontal cortex, and hippocampus to determine whether differences in these structures are related to individual variability in performance. Further, this research tests the hypothesis that a unitary contextual processing mechanism mediated by these dopaminergic neural areas underlies performance on seemingly disparate executive control processes. Indices of inhibition, conflict detection, and source monitoring will be compared to determine whether they activate similar neural structures and to what extent those structures can be considered a correlated circuit.